1. Technical Field of the Invention
This invention relates generally to wireless communication systems and more particularly to radio frequency integrated circuits used in such wireless communication systems.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards, including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, etc., communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of a plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via a public switch telephone network (PSTN), via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it either includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more intermediate frequency (IF) stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more IF stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
As is also known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more IF stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies them. The one or more IF stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or IF signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out-of-band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
The need for wireless networking has been addressed by various standards bodies that promulgate inter-working standards. One such standards body promulgated the IEEE 802.11 standard that defines a wireless LAN. In a typical 802.11 wireless LAN, a wired backbone couples to one or more wireless access points (WAPs) that wirelessly connect to many computers or other electronic devices that contain wireless interfaces. IEEE 802.11 networks have achieved significant success in servicing wireless communication needs for portable computers, portable data terminals, and other wireless devices that transmit and receive data. However, IEEE 802.11 networks lack high data rate and Quality of Service (QOS) features to support multimedia communications.
Wireless personal area networks (WPANs) enable short-range “ad-hoc” connectivity among portable consumer electronics and communication devices but do not require the infrastructure needed for an 802.11 network. The WPAN™ Study Group (SG) was formed on Mar. 12, 1998 by the IEEE 802.11 Working Group to investigate the need for a supplemental wireless network standard specifically targeted to provide very low power consumption, low complexity, wireless connectivity among devices within or entering a Personal Operating Space (POS). This includes devices that are carried, worn, or located near the body. These activities have led to the development of 802.15, which is a WPAN standard.
Another known WPAN is Bluetooth. For both Bluetooth and 802.15 WPANs, the coverage area for a WPAN is generally within a 10-meter radius. In other words, a personal operating space (POS) is the space about a person that typically extends up to 10 meters in all directions and envelops the person whether stationary or in motion. It is within the POS that the portable device communicates with an access point. The Bluetooth radio system has emerged as the first technology addressing WPAN applications with its salient features of low power consumption, small package size, and low cost. Raw data rates for Bluetooth devices are limited to 1 Mbps, although the actual throughput is about half of the raw data rate. A Bluetooth communication link supports up to three voice channels with very limited additional bandwidth for bursty data traffic. However, Bluetooth communication links cannot support the data transfer requirements of portable consumer electronics devices that transmit and receive multimedia data, e.g., high quality video applications, audio applications, and multi-megabyte file transfers for music and image files.
Additional limitations placed upon such devices relate to their cost and power consumption. Many devices operating in an ad-hoc network are battery powered. Thus, the power consumption requirements placed on the device by the integrated circuitry servicing its communications should be minimal. Further, the communication circuitry contained therein desirably should be high in performance but low in cost. Operationally stable, high data rate communication circuitry, e.g., RF front end circuitry, frequency/phase reference circuitry, etc., are relatively high in cost in terms of IC real estate. Thus, components that are highly stable cannot always be employed. Thus, selected components in a circuit often suffer from RF carrier frequency drift, symbol clock frequency drift, and other synchronization related problems. In order to support high data rate communications, these operational problems must be overcome. Thus, there is a need in the art for wireless communication circuit components that support high data rate communications, that consume little power, and that are relatively inexpensive to produce and operate.
Each of the various stages of the radio receiver, whether its part of Bluetooth or an 802.15 WPAN, an 802.11 wireless local area network, or a cellular radio network, consume differing amounts of power but often operate on battery power. Because it is desirable to extend battery life to a maximum amount, many different communication devices provide for a sleep mode in which a radio is powered down until activated by the depression of a key or the like. Moreover, some of the standards provide for powering down a receiver for a specified period of time or mode of operation and then powering the receiver back up to enable it to engage in communications. The standards generally specify a settle time requirement wherein powered down elements must reach an operational steady state within the specified settle time. The frequent power down and power up cycles, among other operations, can generate high frequency noise (transients of short duration and relatively high amplitude), however, as the digital and analog elements change state in response to a power management commands. The high frequency noise can be coupled to the biasing lines that provide power to all elements in the circuit. The biasing lines, therefore, require filtering to bypass this high frequency noise to circuit common.
Accordingly, a need exists for a bias filtering method and circuit that meets the fast settle time requirements of the power management mode of operation and also meets the biasing lines filter requirement.